The MgO thickness dependence of Hanle signals in Co₅₀Fe₅₀/MgO/n-Si tunnel junctions was investigated using a three-terminal geometry. The observed Hanle signal is several orders of magnitude stronger than the predicted value by conventional theory as reported in many literatures. Furthermore, the magnitude of the spin signal depends on the junction resistance rather than the channel resistance, implying that the largest part of the observed Hanle signal is not caused by spin accumulation in the semiconductor region. A possible origin of the observed strong Hanle signal is due to a modulation of the tunneling resistance by a magnetic field, which is induced by the spin precession in localized states formed in the vicinity of the Co₅₀Fe₅₀/MgO interface.

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Based on two different experiments and an optical field calculation, we show that the free‐carrier absorption α_fc in Zn(Cd)Se/ZnMgSSe semiconductor lasers is about 4 cm⁻¹ and that it is smaller than that of GaAs/AlGaAs semiconductor lasers. We have measured the dependence of the L‐I characteristics on the cavity length of double heterostructure (DH) lasers under photopumped operation and of single quantum well‐separate confinement heterostructure (SQW‐SCH) lasers under current‐injected operation. For the DH laser, the total absorption coefficient α_i and β×J₀ product (β is a gain constant, and J₀ is the nominal current density that makes the gain equal to zero) are estimated to be 4.2 cm⁻¹ and 8.6×10 cm⁻¹, respectively. For the SQW‐SCH laser, α_i, β, and J₀ are estimated to be 21 cm⁻¹, 4.23×10⁻³ cm×μm/A, and 1.9×10⁻³ A/(cm²×μm), respectively. By calculating the optical fields of these lasers, we have estimated that the absorption in a GaAs substrate is 16.53 cm⁻¹ in the SQW‐SCH laser and that it is negligible in the DH laser. We have shown that the large loss in the SQW‐SCH laser is caused by both α_fc and the absorption in the substrate and that α_i in the DH laser is caused only by free carrier absorption.

Using amphoteric native defect model [Walukiewicz, Phys. Rev. B 37, 4760 (1988)], we have considered the energy‐gap E_g dependence of nitrogen doping in ZnMgSSe semiconductors. We have explained the energy‐gap E_g dependence of saturated hole concentration in ZnMgSSe semiconductors based on the amphoteric native defect model and available effective hole masses in ZnSe using the valence band discontinuity ΔE_v as a fitting parameter. The Fermi‐level stabilization energy E_FS and the pinned Fermi‐level energy E_SI are, to a good approximation, universal for II‐VI materials as well as for III‐V materials. We have estimated the E_SI is located at 1.895 eV below E_FS. It is indicated that the band‐gap discontinuity between ZnSe and ZnMgSSe is ΔE_c: ΔE_v=0.55:0.45 if effective hole mass is 1.4 m₀ for ZnMgSSe and ΔE_c:ΔE_v=0.67:0.33 if effective hole mass is 0.6 m₀.

Recent progress in blue laser diodes has necessitated the development of ultra-high density mastering corresponding to a density several times higher than that of the digital versatile disk (DVD). As reported earlier, we developed a deep UV master recorder using an all-solid-state 266 nm laser, and confirmed an acceptable RF signal read-out quality from 20 Gbytes capacity with CD disc size, of which the bit density is equal to 14 Gbit/inch². Here, we report the improvement of RF signal jitter utilizing a write compensation technique for the mastering process. In this technique, the positions of the leading and trailing edges of the signal are shifted by pit signal processing (PSP). We confirmed an improved quality read-out signal of which the bottom jitter value is less than 8% from the 20 Gbytes disc, and also analyzed the signal jitter elements. In addition, experimental results of significantly higher densities of up to 30 Gbytes (21 Gbit/inch²) are demonstrated.

The deep UV mastering process of the next generation high density disk is demonstrated for the first time using an all-solid-state continuous-wave 266 nm laser. We have developed a novel deep UV master recorder with a laser source, and achieved a density of 20 Gbytes capacity (14 Gbit/inch²) with acceptable jitter for the compact disk size.